I had the chance to play with mod_rails this weekend and I have to say that it is pretty nice. While I’m not 100% sure I’d use it for a large site (think twitter), I will definitely start using it for some of my smaller sites to start out
If you aren’t familar with mod_rails (or Phusion Passenger) it is a module for Apache. Most of us use Apache all the time, so I’m not going to explain what that is. :P What mod_rails allows you to do, once installed and running, is create a virtual host and map it to the /public folder of your rails app. Then when the domain/URL is accessed, it will go start up a few instances of running a rails app (this is “magic”) and will show your site. If you don’t have a lot of visitors, or currently are the only one accessing the site, the first time might take a little bit (if you don’t configure anything) much like what fcgi does. It is however, faster that fcgi with comparable speeds to mongrel.
Mod_Rails currently does not work on Windows Servers (but who uses them anyways :) ) so you’ll have to make sure that you are using a linux box. There is a good amount of documentation about it, and makes deploying your apps easy.